A satellite navigation system is a satellite based radio-navigation system in which a plurality of satellites orbit the earth and broadcast information that can be used by receivers on the earth to determine a position relative to the satellites. Example satellite navigation systems include the global positioning system (GPS), the GLONASS system, the Beidou navigation system, and the Galileo positioning system.
A satellite navigation system receiver (also referred to herein as simply “receiver”) can determine a navigation solution based on pseudoranges to a plurality of navigation satellites. A pseudorange can be determined based on the time it takes for a signal to propagate from a navigation satellite to the receiver. In order to improve measurement accuracy for the propagation time of the signal, a receiver can compensate for delay experienced by a signal due to atmospheric effects. One of the delays experienced by a signal is caused by traveling through the ionosphere, and is accordingly referred to as “ionospheric delay”.
Receivers that operate below the ionosphere (e.g., on the ground) can utilize Klobuchar's model to estimate the ionospheric delay. In the GPS, parameters are transmitted from GPS satellites for use by receivers in calculating the ionospheric delay according to Klobuchar's model. Accordingly, receivers can calculate the ionospheric delay according to Klobuchar's model based on the parameters transmitted by the GPS satellites. Klobuchar's model calculates ionospheric delay corresponding to a signal that propagated from a satellite to a location below the ionosphere. That is, Klobuchar's model can be used to calculate an ionospheric delay corresponding to a signal having propagated through the entire ionosphere (e.g., a receiver on the ground).
Other models exist to calculate ionospheric delay for a receiver within the ionosphere, that is, to calculate ionospheric delay for a single propagating through only a portion of the ionosphere. These models include a correction model presented by Montenbruck. The Montenbruck model can use curve fitting in order to calculate the ionospheric delay.